Solid electrolyte capacitor

ABSTRACT

A solid electrolytic capacitor of the present invention includes a sheet of valve metal, of which a part constitutes an positive electrode, a dielectric layer formed on a surface of the valve metal, a solid electrolyte layer formed on the dielectric layer, a negative electrode formed on the solid electrolyte layer, and an insulating protective layer for protecting the positive electrode, the dielectric layer, the solid electrolyte layer and the negative electrode. It is further provided with a bump formed on the insulating protective layer and connected to at least one of the positive electrode and the negative electrode. The solid electrolytic capacitor of the present invention is useful to constitute a semiconductor device or a circuit having outstanding high frequency response.

FIELD OF THE INVENTION

The present invention relates to solid electrolytic capacitors used in avariety of electronic devices, and particularly to those on whichsemiconductor devices can be directly mounted.

BACKGROUND OF THE INVENTION

A solid electrolytic capacitor of the prior art comprises a dielectricoxide layer formed on a surface of a positive electrode deviceconsisting of a sheet of valve metal such as aluminum or tantalum, asolid electrolyte layer such as functional polymer and manganese dioxidedisposed on the oxide layer, and a negative electrode layer disposed onan outer surface of the solid electrolyte layer. All of them are moldedentirely thereafter by an outer molding resin, and terminal electrodesare disposed to both ends of the outer molding resin.

The above-described solid electrolytic capacitor of the prior art is aone-chip type component similar to a resistor and inductance componentthat is mounted on a circuit board when being used.

However, although there has been a demand for electronic componentshaving good high frequency response according to a digitization ofcircuits in these days, the conventional solid electrolytic capacitorsof the above kind that are surface-mounted on a circuit board togetherwith semiconductor devices had a problem that they lower the highfrequency response of the circuits.

The present invention is intended to eliminate the above problem of theprior art, and to provide solid electrolytic capacitors that can bedirectly bump-connected with semiconductor devices, and also has asuperior high frequency response.

SUMMARY OF THE INVENTION

A solid electrolytic capacitor of the present invention comprises:

a positive electrode disposed on one side of a sheet of valve metalhaving a dielectric layer formed on its surfaces as well as surfaces ofinternal pores;

a solid electrolyte layer and a negative electrode layer disposed on thedielectric layer of valve metal;

an insulating protective layer provided on their exterior surfaces, atleast one surface of this insulating protective layer is provided with avia hole extending to the positive electrode and the negative electrodelayer;

a conductor connected electrically to one of the electrodes butinsulated from the other provided in the via hole; and

a connecting bump disposed on the conductor exposed on the insulatingprotective layer for connection with a semiconductor device, a chipcomponent, and the like.

By using the solid electrolytic capacitor of present invention, avariety of chip components including semiconductor devices can bemounted to the connecting bumps on the surface of the solid electrolyticcapacitor, and a semiconductor device or a circuit having an outstandinghigh frequency response can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a solid electrolytic capacitor accordingto an exemplary embodiment of the present invention;

FIG. 2 is a sectional view of the same;

FIG. 3 is a sectional view of a sheet of valve metal used for the solidelectrolytic capacitor;

FIG. 4 is a sectional view of the sheet of valve metal having a positiveelectrode formed on it;

FIG. 5 is a sectional view of the sheet of valve metal with resistlayers formed on both surfaces thereof;

FIG. 6 is a sectional view of the sheet of valve metal having via holesformed in it;

FIG. 7 is another sectional view with insulating layers formed in thevia holes;

FIG. 8 is a sectional view of the sheet of valve metal with a resistlayer removed from one of its surfaces;

FIG. 9 is a sectional view of the sheet of valve metal having adielectric oxide layer and a solid electrolyte layer formed thereon;

FIG. 10 is a sectional view of the sheet of valve metal having anegative electrode layer formed on it;

FIG. 11 is a sectional view of the sheet of valve metal having aninsulating protective layer formed on it;

FIG. 12 is a sectional view of the sheet of valve metal with conductorsformed in the via holes;

FIG. 13 is a sectional view of the sheet of valve metal with connectingbumps formed on the conductors;

FIG. 14 is a sectional view of the same with terminals formed on it; and

FIG. 15 is a sectional view showing another sheet of valve metal.

THE BEST MODES FOR CARRYING OUT THE INVENTION

A solid electrolytic capacitor of the present invention will bedescribed hereinafter with reference to FIG. 1 through FIG. 15.

FIG. 1 is a perspective view of a solid electrolytic capacitor accordingto one exemplary embodiment of this invention, and FIG. 2 is a sectionalview of the same solid electrolytic capacitor.

In FIG. 1 and FIG. 2, sheet 1 of valve metal such as aluminum foil orsintered body of valve metal powder such as tantalum, of which onesurface is etched, is provided with positive electrode 2 on thatsurface. If the sheet is made of aluminum foil, an unetched surface ofit may be used as the positive electrode 2, or another metal layercomposed of gold, copper, nickel, arid the like may be formed on it. Ifthe sheet is sintered body of valve metal powder, one surface of thesintered body, on which a dielectric layer is not formed, may be used asis. Or, a metal layer of gold, copper, nickel, tantalum, and the likemay be formed by such a method as sputtering, vacuum deposition, and thelike.

In addition, the sheet 1 is anodized to form dielectric layer 3 onsurfaces of the sheet as well as surfaces of internal pores, with anexception of the positive electrode 2. Solid electrolyte layer 4 is alsoformed on the dielectric layer 3. The solid electrolyte layer 4 can beformed by such means as chemical polymerization and electrolyticpolymerization of electro-conductive polymer such as polypyrrole,polythiophene, and the like, or by forming a manganese dioxide layer byimpregnating the sheet with manganese nitrate solution, followed bythermal decomposition.

Negative electrode layer 5 is formed on the solid electrolyte layer 4.The negative electrode layer 5 may be formed by bonding a metallic foilsuch as copper, or by coating electrically conductive paste on the solidelectrolyte layer 4. Insulating protective layer 6 for covering thementirely is formed by such means as molding, coating, and dipping usingepoxy resin, for instance, or the like.

Via holes 7 are provided in one side of the insulating protective layer6 on the positive electrode 2, and via holes 8 are provided through theinsulating protective layer 6, positive electrode 2, valve metal sheet1, dielectric layer 3, and solid electrolyte layer 4. The via holes 7and 8 are formed by laser beam irradiation, etching, punching, or thelike process.

Insulating layer 9 is formed on every inner wall of the via holes 8.Conductors 10 are formed in the via holes 7 and 8 by copper plating orthe like. The conductors 10 in the via holes 7 and the conductors 10 inthe via holes 8 are electrically connected to the positive electrode 2and the negative electrode layer 5 respectively.

There are connecting bumps 11 formed of solder, gold, tin, silver, andthe like on top of the conductors 10 on a surface of the sheet. A numberof the connecting bumps 11 to be formed and their pitches are the sameas the number and pitch of connecting bumps of a semiconductor device tobe mounted afterward, or the former number may be larger than the latternumber. The reason of forming the larger number of connecting bumps 11than that of the connecting bumps of the semiconductor device is to makeit possible to mount chip components such as chip resistors, chipceramic capacitors, as well as chip inductors and the like between theremaining connecting bumps 11, after the semiconductor device ismounted.

In addition, terminals 12 and 13 connected respectively with thepositive electrode 2 and the negative electrode layer 5 are formed onside surfaces and a bottom surface of the insulating protective layer 6.

Thus, a semiconductor device produced in this manner by mounting asemiconductor and the like device directly on one surface of the solidelectrolytic capacitor eliminates a pattern of wiring conductors on acircuit board, and thereby substantially improves the high frequencyresponse of the semiconductor device.

Besides, if aluminum foil, one surface of which is etched, is used forthe sheet 1, already established manufacturing facilities, productiontechniques, and know-how concerning aluminum foil for the aluminumelectrolytic capacitors can effectively be used. That is, sheet 1 havingthe desired etched pits can be obtained readily only if one surface ofthe aluminum foil is masked and etched, so as to improve productivity ofthe solid electrolytic capacitors without making new investment onplant.

Furthermore, an electrostatic capacity of the solid electrolyticcapacitor can be increased when sintered body of valve metal powder suchas tantalum is used as the sheet 1.

Moreover, if one surface of the aluminum foil or sintered body of valvemetal powder is used as positive electrode 2, another metal layer is notneeded to serve as the positive electrode 2. This reduces the componentparts and improves efficiency in production, thereby giving it anadvantageous in terms of cost. However, it is preferable to form a metallayer of such as gold, copper, nickel and the like for use as thepositive electrode 2 on a surface of the sheet 1 in order to improve aconnection reliability between the conductors 10 formed in the via holes7 and 8 and the positive electrode 2.

Also, a use of electro-conductive polymer such as polypyrrole andpolythiophene as the solid electrolyte layer 4 makes it possible toobtain a solid electrolytic capacitor of low impedance, i.e., the solidelectrolytic capacitor with outstanding high frequency response.

In addition, as the fully established technique, there is a method offorming manganese dioxide for use as the solid electrolyte layer 4. Inthe case of forming manganese dioxide, the accumulated technique of theprior art can be applied to produce a dense solid electrolyte layer. Italso improves productivity as well as reliability because it is capableof controlling thickness of the solid electrolyte layer 4.

In the foregoing embodiment, although an example, in which theconnecting bumps 11 are disposed only to one surface of the insulatingprotective layer 6 is described, the connecting bumps 11 may be formedon both surfaces of the sheet 1. In this case, the via holes 7 and 8 areso provided that they reach the negative electrode layer 5 and thepositive electrode 2 respectively, each of the via holes 8 are providedwith insulating layer 9, and conductors 10 are formed in them byplating. The above structure provides a solid electrolytic capacitorwith connecting bumps 11 on both surfaces.

In addition, although the above-described embodiment is an examplehaving the terminals 12 and 13 formed thereon, the terminals 12 and 13are not always necessary. The connecting bumps 11 can be used assubstitutes for the terminals 12 and 13. Further, it is also possible touse a semiconductor device and chip component mounted on the connectingbumps 11 as substitutes for the terminals.

Referring now to FIG. 3 through FIG. 14, one example of a method ofmanufacturing solid electrolytic capacitors of the present inventionwill be described hereinafter.

First, an aluminum foil, of which one surface is etched, is prepared asthe sheet 1, as shown in FIG. 3. This aluminum foil can be obtainedreadily by masking one of the foil surfaces and subjecting it to etchingprocess.

Next, positive electrode 2 consisting of copper is formed on unetchedsurface of the sheet 1, as shown in FIG. 4. This positive electrode 2can be formed by sputtering, vacuum deposition, or bonding a copperfoil.

Then, resist layer 14 of photoresist or masking tape having a resistanceto chemicals is formed on both surfaces as shown in FIG. 5. After theresist layer 14 is cured, a required number of via holes 8 are formed bypunching in required places, as shown in FIG. 6. Thereafter, insulatinglayers 9 are formed on inner walls of the via holes 8 by anelectrodeposition of resin, as shown in FIG. 7.

Following the above, resist layer 14 on a surface opposite the positiveelectrode 2 is stripped off or removed by dissolving, to expose thesurface of the porous sheet 1, as shown in FIG. 8. It is then anodizedin anodizing solution to form dielectric layer 3 on the surface of thesheet as well as surfaces of internal pores, as shown in FIG. 9. Thesheet with the oxidized dielectric layer 3 formed thereon is immersed insolution containing pyrrole, and successively into another solution ofoxidizer, to form a thin polypyrrole layer on the dielectric layer 3 bychemical oxidation polymerization. The sheet having the polypyrrolelayer formed is immersed in the solution containing pyrrole, andelectrolytic polymerization is carried out as the polypyrrole layer andan electrode in the solution as being positive and negativerespectively. This produces another polypyrrole layer of sufficientthickness on the polypyrrole layer described above, to form the solidelectrolyte layer 4.

Thereafter, resin sheet 15 having negative electrode layer 5 of copperformed on one of its surfaces is bonded in such a manner that this metalnegative electrode layer 5 is electrically in contact with the solidelectrolyte layer 4, as shown in FIG. 10. Subsequently, via holes 7 areformed in predetermined locations at the side adjoining the positiveelectrode 2, as shown in FIG. 11. At the same time, insulatingprotective layer 6 consisting of epoxy resin or the like is formed onit, including a side surface, with openings being in communication tothe surface of the positive electrode 2.

Conductors 10 are then formed in the via holes 7 and 8, and in theopenings by plating copper or the like on their inner surfaces, as shownin FIG. 12. In this process, the conductors 10 in the via holes 7 andthe conductors 10 in the via holes 8 are so formed that they areelectrically in contact with the positive electrode 2 and the negativeelectrode layer 5 respectively.

Finally, connecting bumps 11 are formed with solder, gold, tin, orsilver on the conductors 10 exposed above the insulating protectivelayer 6, as shown in FIG. 13. Further, terminals 12 and 13 to beconnected with the positive electrode 2 and the negative electrode layer5 respectively are formed on side surfaces and bottom surface, as shownin FIG. 14, to complete the solid electrolytic capacitor.

In addition, when tantalum foil 16 and sintered body of valve metalpowder are used for the sheet, as another example, sintered body 17 oftantalum is bonded to one side of the tantalum foil 16, as shown in FIG.15, to construct the sheet 1.

A solid electrolytic capacitor is then produced following the sameprocess as in the case of the foregoing embodiment that uses aluminumfoil.

The solid electrolytic capacitor of the present invention, because ofthe above structure, is able to compose a semiconductor device byconnecting a semiconductor directly on a surface of the solidelectrolytic capacitor where the connecting bumps are formed. Since thiscan constitute an electric circuit, or the semiconductor device havingconsiderably superior high frequency response, it can become a usefuldevice in constructing a digital circuit. Accordingly, the solidelectrolytic capacitor of this invention is quite suitable for use in adigital circuit that requires a high-speed response.

What is claimed is:
 1. A solid electrolytic capacitor comprising: aporous body of valve metal, parts of said porous body constituting aplurality of positive electrodes; a dielectric layer formed on a surfaceof said valve metal; a solid electrolyte layer formed on said dielectriclayer; a plurality of cathode electrodes formed on said solidelectrolyte layer; and an insulating protective layer for protectingsaid positive electrodes, said dielectric layer, said solid electrolytelayer, and said cathode electrodes, wherein said solid electrolyticcapacitor has a plurality of bumps formed on said insulating protectivelayer, and connected to at least any of said positive electrodes andsaid cathode electrodes.
 2. The solid electrolytic capacitor accordingto claim 1, wherein said porous body of valve metal is of a sheet form.3. The solid electrolytic capacitor according to claim 1, wherein theconnections between any of said positive electrodes and said negativeelectrodes and said bumps are made through conductors formed in viaholes formed in any of said porous body of valve metal and saidinsulating protective layer.
 4. The solid electrolytic capacitoraccording to claim 1, wherein said porous body of valve metal is asintered body of valve metal powder.
 5. The solid electrolytic capacitoraccording to claim 4, wherein parts of said sintered body where saiddielectric layer is not formed constitute said positive electrodes. 6.The solid electrolytic capacitor according to claim 5 further comprisinga metal layer formed on said positive electrodes.
 7. The solidelectrolytic capacitor according to claim 1, wherein said porous body ofvalve metal is an aluminum foil of which one surface is etched.
 8. Thesolid electrolytic capacitor according to claim 7, wherein an unetchedsurface of said aluminum foil constitutes said positive electrodes. 9.The solid electrolytic capacitor according to claim 8 further comparinga metal layer formed on said unetched surface of said aluminum foil. 10.The solid electrolytic capacitor according to claim 1, wherein saidsolid electrolyte is an electro-conductive polymer.
 11. The solidelectrolytic capacitor according to claim 1, wherein said solidelectrolyte is manganese dioxide.
 12. The solid electrolytic capacitoraccording to claim 1, wherein a number of said bumps is larger than anumber of connecting bumps of a semiconductor device to be connected tosaid solid electrolytic capacitor.
 13. The solid electrolytic capacitoraccording to claim 1, wherein a plurality of solid electrolyticcapacitors are formed on one said porous body of valve metal.
 14. Asolid electrolytic capacitor of unitary capacitor element structurecomprising: a porous body of valve metal, parts of said porous bodyconstituting a plurality of positive electrodes; a dielectric layerformed on a surface of said valve metal; a solid electrolyte layerformed on said dielectric layer; a plurality of negative electrodesformed on said solid electrolyte layer; and an insulating protectivelayer for protecting said positive electrodes, said dielectric layer,said solid electrolyte layer, and said negative electrodes, wherein saidsolid electrolytic capacitor has a plurality of bumps formed on saidinsulating protective layer, and connected to at least any of saidpositive electrodes and said negative electrodes.
 15. A solidelectrolytic capacitor comprising: a positive electrode disposed on onesurface of a porous sheet of valve metal having an oxidized dielectriclayer formed on a surface thereof as well as on surfaces of internalholes; a solid electrolyte layer and a negative electrode layer disposedon another surface of said porous sheet of valve metal; an insulatingprotective layer provided on an exterior surface of said positiveelectrode and said negative electrode; via holes provided in at leastone of surfaces of said insulating protective layer, each of said viaholes extending to one of said positive electrode and said negativeelectrode layer; conductors provided in said via holes, said conductorselectrically connected to any of said electrodes individually butinsulated from the other electrodes; and connecting bumps disposed onexposed surfaces of said conductors.